Heterogeneous catalyst for transesterification and method of preparing same

ABSTRACT

A transesterification catalyst that is heterogeneous and a method for preparing said transesterification catalyst are provided. The catalyst can be used in a variety of transesterification reactor configurations including CSTR (continuous stirred tank reactors), ebullated (or ebullating) beds or any other fluidized bed reactors, and PFR (plug flow, fixed bed reactors). The catalyst can be used for manufacturing commercial grade biodiesel, biolubricants and glycerin.

RELATED APPLICATIONS

This application claims the benefit, and priority benefit, of U.S.Provisional Patent Application Ser. No. 62/149,138, filed Apr. 17, 2015;U.S. Provisional Patent Application Ser. No. 62/155,970, filed May 1,2015 and U.S. Provisional Patent Application Ser. No. 62/320,104, filedApr. 8, 2016 the contents of each of which are incorporated by referenceherein in their entirety.

BACKGROUND

1. Field of the Invention

The presently disclosed subject matter relates to a heterogeneouscatalyst and use of the heterogeneous catalyst for transesterification.

2. Description of the Related Art

Transesterification is the reversible chemical reaction process ofexchanging the organic group of an ester with the organic group of analcohol. Transesterification processes became commercially popular inthe 1940s as researchers explored ways to more readily produce glycerol(also called glycerin, glycerine and propanetriol) used in explosivesmanufacture during World War II. Currently, transesterification is animportant step in industrial processes such as production of: acrylatesfrom methymethacrylate, polyethylene terephthalate (PET) polymermanufacturing from ethylene glycol and either dimethyl terephthalate orterephthalic acid, and alkyl esters. Of particular current commercialinterest is the transesterification of alcohol with triglyceride esterscontained in oils and fats (primarily vegetable oils and animal fats) toform fatty acid alkyl esters and glycerin. These esters find commercialuse as biodiesel fuel and biolubricants.

Catalysts known to facilitate the transesterification reaction includemineral acids and bases, metal alkoxides, non-ionic bases and lipaseenzymes. These catalysts include homogeneous species which are solublein reactants and/or products and heterogeneous species which are solidsand insoluble in reactants or products.

Alkaline metal alkoxides (e.g., CH₃ONa for methanolysis) and alkalinemetal hydroxides (NaOH and KOH) are catalysts for the homogeneoustransesterification reaction. These catalysts are soluble in reactantsand products and thus require extensive post-reaction treatmentincluding product neutralization, salt removal and water wash to producecommercially acceptable products. These are nontrivial processes andcostly to install, maintain and operate. Homogeneous enzymatictransesterification using lipase has been utilized for conversion oftriglycerides to biodiesel, since the byproduct glycerin can be purifiedby flashing off the excess alcohol from the products. However,processing time can be lengthy for acceptable conversion oftriglycerides and product clean-up costs are high to make commercialgrade products.

Replacement of the homogeneous catalyst with heterogeneous catalyst hasbeen commercialized notably with the Esterfip-H® process licensed byAxens and the ENSEL® process licensed by Benefuel. These heterogeneouscatalyst processes can reduce post-reaction processing, but requirereaction operating temperatures of 150 degrees C. to 250 degrees C. andalcohol partial pressure as high as 300 to 400 psi for the manufactureof biodiesel alkyl esters. These heterogeneous catalyst reactions mustbe carried out in fixed bed reactors due to the severity of the processconditions.

Improvements in this field of technology are desired to reduce theoperating severity and costs of the transesterification reaction regimeas well as the subsequent process clean-up and product purificationsteps. Improvements are also desired which allow use of new technologyin existing or readily modified commercial facilities.

SUMMARY

According to the various illustrative embodiments disclosed herein, atransesterification catalyst that is heterogeneous and a method forpreparing said transesterification catalyst are provided. For thepurposes of this disclosure, the transesterification catalysts of thevarious illustrative embodiments will hereinafter be referred to asUMAKAT. Various means for transesterification using UMAKAT are alsoprovided.

In certain illustrative embodiments, UMAKAT can be used in a variety oftransesterification reactor configurations including CSTR (continuousstirred tank reactors), ebullated (or ebullating) beds or any otherfluidized bed reactors, and PFR (plug flow, fixed bed reactors). UMAKATcan be used for manufacturing commercial grade biodiesel, biolubricantsand glycerin.

In certain illustrative embodiments, a compound is provided. Thecompound can have the formula Z_(x)Q_(y)PO_(n)MH₂0, wherein Z isselected from the group consisting of potassium, sodium and lithium, Qis selected from the group consisting of calcium, magnesium and barium,x is a rational number in the range from 0.5 to 4, y is a rationalinteger in the range from 2 to 8, n is a rational integer in the rangefrom 4 to 8, and M is a ceramic substrate, and wherein the compound is atransesterification catalyst. The total surface area of the compound canbe greater than 20 square meters per gram. The active surface area ofthe compound can be greater than 20 square meters per gram. The averagediameter of the pores in the compound can be in the range from 1-10nanometers. The compound can be active at a temperature in the rangefrom 40 to 70 degrees C. The compound can also be active at atemperature in the range from 40 to 130 degrees C.

In certain illustrative embodiments, a method of preparing atransesterification catalyst is provided. A metal hydroxide with themetal selected from the group consisting of potassium, sodium andlithium can be mixed with a metal hydroxide with the metal selected fromthe group consisting of calcium, magnesium and barium. The componentscan be mixed in a ratio of approximately 1:10 by weight to form acomponent mixture, in certain illustrative embodiments. The componentmixture can be dissolved in phosphoric acid and heated to a temperaturein the range from 60-90 degrees C. A solid compound can be precipitatedand washed. The precipitate can be mixed with ceramic substrate powderin a ratio of approximately 2:10 by weight and washed with water. Theprecipitate/ceramic substrate mixture can be calcined. Calcination canoccur at a temperature in the range from 400-500 degrees C. for 4 hoursor greater.

In certain illustrative embodiments, a method of preparing an alkylester using a transesterification catalyst is provided. The alkyl estercan be suitable for use as biodiesel fuel, as a biodiesel additive toconventional diesel fuel, or as a biolubricant additive to conventionallubricants. The alkyl ester can also be suitable for use as abiolubricant. A transesterification catalyst can be provided. Thecatalyst can have the formula Z_(x)Q_(y)PO_(n)MH₂0, wherein Z isselected from the group consisting of potassium, sodium and lithium, Qis selected from the group consisting of calcium, magnesium and barium,x is a rational number in the range from 0.5 to 4, y is a rationalinteger in the range from 2 to 8, n is a rational integer in the rangefrom 4 to 8, and M is a ceramic substrate. Triglycerides and alcohol canbe reacted in the presence of said catalyst to convert the triglyceridesand alcohol to alkyl ester and glycerin. The triglycerides can betriglyceride-containing fats and/or oils. The conversion can beessentially complete conversion of triglycerides. The glycerin can beseparated from the reaction mixture. The reaction mixture can befiltered to recover the catalyst. The unreacted alcohol can be distilledfrom the alkyl ester and the glycerin. The method can be at leastpartially performed in a continuous stirred tank reactor. The method canalso be at least partially performed in a fixed bed reactor. The methodcan also be at least partially performed in a fluidized bed reactor. Thealkyl ester is capable of being used as biodiesel fuel, a biodieseladditive to conventional diesel fuel, a biolubricant additive to otherlubricants or as a biolubricant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show an illustrative embodiment of a transesterificationreaction.

FIG. 2 is a line graph comparing reaction conversion at differentmethanol molar ratios at 1 weight % of UMAKAT in an illustrativeembodiment.

FIG. 3 is a line graph comparing reaction conversion at differenttemperatures at 1 weight % of UMAKAT in an illustrative embodiment.

FIG. 4 is a line graph comparing reaction conversion at different UMAKATweights at a fixed temperature of 60 degrees C. in an illustrativeembodiment.

FIG. 5 is a line graph comparing biodiesel (i.e., alkyl ester) yieldusing the same UMAKAT for repeat trials in an illustrative embodiment.

While certain preferred illustrative embodiments will be describedherein, it will be understood that this description is not intended tolimit the subject matter to those embodiments. On the contrary, it isintended to cover all alternatives, modifications, and equivalents, asmay be included within the spirit and scope of the subject matter asdefined by the appended claims.

DETAILED DESCRIPTION

For the purposes of this disclosure, the transesterification catalystsof the various illustrative embodiments will hereinafter be referred toas UMAKAT. Various means for transesterification using UMAKAT are alsoprovided. According to the various illustrative embodiments providedherein, UMAKAT is a porous, solid, heterogeneous compound having thegeneral formula Z_(x)Q_(y)PO_(n)MH₂0, where Z is selected from Group 1metals including potassium, sodium and lithium, Q is selected from Group2 metals including calcium, magnesium and barium, x is a rational numberin the range from 0.5 to 4, y is a rational integer in the range from 2to 8, and n is a rational integer in the range from 4 to 8. M can be anyceramic substrate such as, for example, zirconia, silica, alumina, orcombinations thereof. The Group 1 and Group 2 alkali metals form adouble metal salt catalyst, the phosphate (PO_(O)) makes it insolubleand the ceramic provides the solid support, in certain illustrativeembodiments. UMAKAT's porous structure includes nanometer-sized poreswhich result in the material having substantial surface area.

The generic process for the transesterification reaction is shown inFIGS. 1A and 1B. FIG. 1A represents the overall transesterificationreaction, while FIG. 1B represents not only the overall reaction butalso the stepwise chemical reactions where the triglyceride (TG) esteris first converted to alkyl ester and diglyceride (DG) ester, then theDG ester is converted to alkyl ester and monoglyceride (MG) ester, andthen the MG ester is converted to alkyl ester and glycerin.

In certain illustrative embodiments, UMAKAT can have a total surfacearea greater than 20 m²/gm and an active surface area greater than 20m²/gm. As used herein, the term “total surface area” means surface areatotally available, and the term “active surface area” means surface areaavailable for reaction. The active surface area of UMAKAT is significantbecause the higher the active surface area, the greater the availabilityof active catalyst sites. Total surface area and active surface area aremeasured by nitrogen adsorption.

In certain illustrative embodiments, the heterogeneous compound can beporous. For example, UMAKAT can have an average pore diameter in therange from 1-10 nanometers (Nm). Pore diameter is measured by nitrogenadsorption. The pore diameter of UMAKAT is sufficient to allow migrationor diffusion of reactant molecules into and out of the UMAKAT pores, incertain illustrative embodiments. This will determine the rate andextent of absorption of reactant molecules at the catalyst surfaces.

Other homogeneous transesterification processes call for the catalystbeing dissolved in an alcohol, for example, methanol or ethanol, whichneeds to be removed post reaction. Further, the homogeneous catalyst issoluble in reactants and products, which requires steps to cleanse thealkyl ester and glycerin products. In contrast, in certain illustrativeembodiments UMAKAT can form a slurry with triglyceride-containing oilsand/or fats rather than alcohol for a better reaction conversion andeasier separation of reactants and catalyst at the end of the reaction.In general, a catalyst slurry can be made with any oil/fat rather thanmethanol/ethanol solution (or any other alcohol) for CSTR typereactions. Further, in certain illustrative embodiments UMAKAT providesa uniform suspension throughout the reaction media. By comparison, aheterogeneous catalyst suspension in methanol/ethanol is not uniform andthe catalyst particles settle at the bottom of the reactor vessel.

In certain illustrative embodiments, UMAKAT can be active atsignificantly less severe conditions than other heterogeneous catalystsystems. For example, other methanolysis transesterificationheterogeneous catalysts require temperatures from 150 to 250 degrees C.and pressures of 300 to 400 psi. These operating conditions require thatother processes using heterogeneous catalysts are carried out in fixedbed reactors.

In contrast, methanolysis transesterification using UMAKAT tomanufacture biodiesel requires temperatures in the range from 40 to 70degrees C. and atmospheric pressure conditions, in certain illustrativeembodiments. Similarly, transesterification using UMAKAT to react, forexample, dodecanol or other higher alcohols and triglycerides tomanufacture biolubricants requires temperatures up to and slightly above100 degrees C. and atmospheric pressure conditions, in certainillustrative embodiments. For these services, UMAKAT can be used inCSTR, fluidized bed and PFR reactor systems.

To ensure complete conversion of triglycerides, alcohol is added inexcess of stoichiometric requirements, for instance 2 to 4 times thatrequired to ensure the complete conversion of triglycerides to alkylester, in certain illustrative embodiments.

Furthermore, UMAKAT is an efficient catalyst in that it can be reusable.UMAKAT can also be used in existing transesterification processequipment without major revamping.

UMAKAT can be used for manufacturing ASTM D 6751 biodiesel and TechnicalGrade glycerin as well as biolubricants. Also, UMAKAT does not needwater wash for post reaction treatment and does not require steps suchas pH neutralization to cleanse products.

In order to facilitate a better understanding of the presently disclosedsubject matter, the following examples of certain aspects of certainembodiments are given. In no way should the following examples be readto limit, or define, the scope of the presently disclosed subjectmatter.

Example 1

UMAKAT preparation is illustrated as a double metal salt catalyst withceramic base support of zirconium oxide. In a typical catalystpreparation, 3 moles of Group 1 metal hydroxide, in this Examplepotassium hydroxide, is mixed with 1 mole of a Group 2 metal hydroxide,in this Example calcium hydroxide, and dissolved in dilute phosphoricacid. The reaction of the metal hydroxides and the acid produces adouble metal salt. This is then heated in a temperature range from 60 to90 degrees C. As a result, a white precipitate is formed which is thenwashed with water and mixed with 4 moles of zirconium oxide powder. Thismaterial is calcined at 400-500 degrees C. for a minimum of 4 hours. Theresulting material is porous, solid and heterogeneous withnanometer-sized pores with a structure that has significant surfacearea.

Example 2

This example describes the preparation of fatty acid methyl esters bytransesterification of soybean oil with methanol using UMAKAT. In atypical reaction, commercial soybean oil (100 gms) and methanol (oil tomethanol molar weight ratio of 1:6) and UMAKAT (2 to 6 wt % UMAKAT inoil) were charged to a 500 ml glass beaker and stirred at a speed of 300to 500 rpm at a temperature of 60-80 degrees C. for about 10 to 30minutes. It was then allowed to cool.

The UMAKAT was separated by filtration from the mixture of reactionproducts. The product mixture included unreacted methanol plus an upperlayer of methyl ester and a lower layer of glycerin. Then, unreactedmethanol was separated from each layer by distillation. The methyl esterwas tested in a gas chromatograph.

The methyl ester analysis report is summarized in Table 1 below alongwith the ASTM spec for biodiesel.

TABLE 1 UMAKAT ASTM SPEC Water & Sediment 0.000 .05 max Cetane Number47.8 47 min Cold Soak Filtration 90 seconds for 300 ml 300 sec max Freeglycerin 0.005% .02 max Total glycerin 0.191% .24 max Calcium, ppm <1 —Magnesium, ppm <1 — Sodium, ppm <1 — Potassium, ppm <2 —

Table 1 generally shows: no water and sediments are present in the alkylester product, only trace amounts of metals solids are present, and, asmeasured by the amount of glycerin in the product, the reaction isessentially complete conversion to methyl ester. The biodiesel made withUMAKAT was also assessed via the Cold Soak Filtration Test. In thistest, a biodiesel liquid sample is chilled to below 32 degrees F. for 16hours, restored to room temperature and passed thru a 0.5 micron filter.This ASTM test is passed if the filtration is complete within 300seconds. The UMAKAT biodiesel passed thru the filter in 90 seconds.

Different oils and fats were tested for oil conversion to methyl esterusing UMAKAT and the results are tabulated in the following table:

TABLE 2 Test % Oil No. Oil/Fat Alcohol conversion Notes 2 Canola OilMethanol 97.7 — 3 Yellow grease Methanol 96.8 — 4 Coconut Oil Methanol98.2 — 5 Cottonseed Oil Methanol 97.5 — 6 Chicken Fat Methanol 97.2 HighFree Fatty Acid (“FFA”) Oil first esterified with acid catalyst

Table 2 shows that UMAKAT is effective for a wide variety of oils andfats.

FIGS. 2 thru 5 are heterogeneous catalytic kinetics graphs showing howthe reaction proceeds at different temperatures, methanol ratios, andcatalyst weight concentrations.

In certain illustrative embodiments, UMAKAT can be easily separated fromreactants and products and reused, no leaching of metal ions into thereactant mixture was observed, and UMAKAT processing temperature andpressure are at moderate conditions which are significantly less severethan other heterogeneous catalytic transesterification processes.

Additionally, in certain illustrative embodiments UMAKAT can be used toprocess low cost/unrefined oils and/or fats containing impurities that,for example, cause discoloration of the feedstock. Further, postreaction process waste is reduced as neutralization and water wash ofproducts are not required. Relative to other catalysts and processes,UMAKAT is highly active at comparatively low temperature and pressure.Also, UMAKAT produces much fewer impurities in the alkyl ester andglycerin products and thus the products are much cleaner at the end ofthe reaction. Further, no pH neutralization water wash is required andsalts from glycerin neutralization do not end up in the alcoholdistillation column. Finally, UMAKAT transesterification facilities arecomparatively lower in cost to install, maintain and operate.

As used herein, the term “in the range from” and like terms is inclusiveof the values at the high and low end of said ranges, as well asreasonable equivalents.

While the disclosed subject matter has been described in detail inconnection with a number of embodiments, it is not limited to suchdisclosed embodiments. Rather, the disclosed subject matter can bemodified to incorporate any number of variations, alterations,substitutions or equivalent arrangements not heretofore described, butwhich are commensurate with the scope of the disclosed subject matter.

Additionally, while various embodiments of the disclosed subject matterhave been described, it is to be understood that aspects of thedisclosed subject matter may include only some of the describedembodiments. Accordingly, the disclosed subject matter is not to be seenas limited by the foregoing description, but is only limited by thescope of the appended claims.

What is claimed is:
 1. A compound having the formula:Z_(x)Q_(y)PO_(n)MH₂0, wherein: Z is selected from the group consistingof potassium, sodium and lithium, Q is selected from the groupconsisting of calcium, magnesium and barium, x is a rational number inthe range from 0.5 to 4, y is a rational integer in the range from 2 to8, n is a rational integer in the range from 4 to 8, and M is a ceramicsubstrate; and wherein the compound is a transesterification catalyst.2. The compound of claim 1, wherein the ceramic substrate is selectedfrom the group consisting of zirconia, silica, alumina, and combinationsthereof.
 3. The compound of claim 1, wherein the total surface area ofthe compound is 20 square meters per gram or greater.
 4. The compound ofclaim 1, wherein the active surface area of the compound is 20 squaremeters per gram or greater.
 5. The compound of claim 1, wherein theaverage diameter of the pores in the compound is in the range from 1-10nanometers.
 6. The compound of claim 1, wherein the compound is activeat a temperature in the range from 40 to 70 degrees C.
 7. The compoundof claim 1, wherein the compound is active at a temperature in the rangefrom 40 to 130 degrees C.
 8. The compound of claim 1, wherein thetransesterification catalyst is porous.
 9. A method of preparing atransesterification catalyst comprising: mixing a metal hydroxide withthe metal selected from the group consisting of potassium, sodium andlithium with a metal hydroxide with the metal selected from the groupconsisting of calcium, magnesium and barium in a ratio of about 1:10 byweight to form a component mixture; dissolving the component mixture inphosphoric acid; heating the component mixture to a temperature in therange from 60-90 degrees C.; precipitating a solid compound; mixing theprecipitate with ceramic substrate in a ratio of about 2:10 by weightand washing with water to form a precipitate/ceramic substrate mixture;and calcining the precipitate/ceramic substrate mixture at a temperaturein the range from 400-500 degrees C.
 10. The method of claim 9, whereinthe precipitate/ceramic substrate mixture is calcined by heating forfour hours or greater.
 11. A method of preparing alkyl ester using atransesterification catalyst, the method comprising: providing atransesterification catalyst comprising a compound having the formulaZ_(x)Q_(y)PO_(n)MH₂0, wherein: Z is selected from the group consistingof potassium, sodium and lithium, Q is selected from the groupconsisting of calcium, magnesium and barium, x is a rational number inthe range from 0.5 to 4, y is a rational integer in the range from 2 to8, n is a rational integer in the range from 4 to 8, and M is a ceramicsubstrate; and reacting one or more triglycerides and an alcohol in thepresence of the catalyst and converting the triglycerides and alcohol toalkyl ester and glycerin.
 12. The method of claim 1, wherein the ceramicsubstrate is selected from the group consisting of zirconia, silica,alumina, and combinations thereof.
 13. The method of claim 11, whereinthe triglycerides comprise triglyceride-containing fats and/or oils. 14.The method of claim 11, wherein the converting of triglyceridescomprises producing essentially complete conversion of the triglyceridesto alkyl ester and glycerin.
 15. The method of claim 11, furthercomprising: separating the glycerin from the reaction mixture; filteringthe reaction mixture to recover the catalyst; and distilling theunreacted alcohol from the alkyl ester and the glycerin.
 16. The methodof claim 11, wherein the method is at least partially performed in acontinuous stirred tank reactor.
 17. The method of claim 11, wherein themethod is at least partially performed in a fixed bed reactor.
 18. Themethod of claim 11, wherein the method is at least partially performedin a fluidized bed reactor.
 19. The method of claim 11, wherein thealkyl ester is capable of being used as biodiesel fuel.
 20. The methodof claim 11, wherein the alkyl ester is capable of being used asbiodiesel additive to conventional diesel fuel.
 21. The method of claim11, wherein the alkyl ester is capable of being used as a biolubricantadditive to other lubricants.
 22. The method of claim 11, wherein thealkyl ester is capable of being used as a biolubricant.